A Model of Initial Failure in Slab-Avalanche Release

At strain-rates below 1 × 10 −4 s −1 , low-density weak seasonal snow fails in a ductile manner. In inclined natural snow covers, local strain-rates hardly ever exceed 1 × 10 −4 s −1 , therefore initial shear failure, which eventually starts slow and finally fast fracture propagation causing slab releases, must be ductile. Changes in initial stability during precipitation periods are simulated using a microscopic mechanical model for weak low-density snow combined with equations describing strength increase by settling and sintering as a function of snow temperature. The results indicate, in good correspondence with experience, a strong dependence of fracture height of direct-action avalanches on precipitation intensity, snow temperature, and slope angle.